It is known in the art to bond polyvinyl butyral material to a coated glass substrate, wherein the coating comprises an electrically conductive, transparent metal-based coating. Exemplary of this technology are heated glass vision units such as are known for use in motor vehicles as electrically heated windshields (hereinafter sometimes referred to as "an EHWS"). In an EHWS a layer of polyvinyl butyral material, typically polyvinyl butyral with such additives as plasticizers and the like, is laminated between a first, outboard glass template and a second, inboard glass template. The inside surface of a outboard glass template carries an electrically conductive, transparent, metal-based coating which directly contacts and is adhered to the polyvinyl butyral interlayer. As used herein the term "metal-based coating" means a coating which comprises, or a layer of which comprises, metal and metal oxide components. The term "transparent" is used herein to means substantially transparent to radiation in the visible wave length band. Substantially transparent means complying at least with applicable regulations, such as those applicable to motor vehicle windshields.
It is a recognized objective in the art to control and improve the adhesion at the interface of the coated glass substrate and the adhered polyvinyl butyral material. Thus, regarding particularly an EHWS, it is desirable to control and improve the adhesion of polyvinyl butyral material to the surface of the glass template which carries the electrically conductive, transparent, metal-based coating thereon. In this particular application and like applications wherein the polyvinyl butyral material is bonded to the coated glass substrate in a laminating operation using heat and pressure, the adhesion at such interface must be compatible with the laminating operation so as to be operative and effective in the laminated assembly.
Further, the adhesion must be durable in the environment in which the article will be used. It is now recognized to be desirable to increase the durability or stability of the polyvinyl butyral interfacial bond against the effects of prolonged exposure to UV radiation. A motor vehicle windshield, for example, typically is subjected to prolonged exposure to UV radiation as a component of sunlight. The mechanism by which prolonged exposure to UV radiation deteriorates the interfacial bond is not completely understood and, in part for this reason, there was prior to this invention no obvious means by which the UV radiation resistance of such interfacial bond could be increased. That is, prior to this invention there was no known or predictable, technologically feasible means to achieve increased resistance to UV radiation.
It is, therefore, an object of the present invention to improve the adhesion at the interface between polyvinyl butyral material and an electrically conductive, transparent, metal-based coating on a surface of a glass substrate. It is a particular object to improve the durability of such bond against exposure to UV radiation. This and other objects of the invention will be understood by the skilled of the art in the light of the following disclosure of the invention.